1. Field of the Invention
The present invention relates generally to the transportation of radiation, and more specifically to the use of optical fiber bundles in the transportation of radiation.
2. Technical Background
Ultraviolet radiation finds wide application a diverse array of technologies. For example, the semiconductor industry uses ultraviolet radiation in photolithographic processes to define the conductive paths in integrated circuits. The lower limit of feature size is directly related to the wavelength of the radiation; hence, to form smaller features, it is desirable to use shorter wavelength radiation. Likewise, in metrology applications it is desirable to use radiation having as short a wavelength as possible to maximize resolution. Ultraviolet radiation also finds use in medical and industrial applications.
While ultraviolet radiation is extremely useful, there exist few workable methods to transport it from one location (i.e. the source) to another (i.e. an instrument or a workpiece). Lenses and mirrors may be used to reflect and focus the radiation; such apparati are difficult to align, sensitive to vibrations, require highly specialized and expensive materials, and may cause exposure of personnel to the radiation. Better methods for transporting ultraviolet radiation are needed in the art.
In ultraviolet photolithography applications, the polarization of the beam as it strikes the wafer can have an effect on the image contrast and the smallest obtainable feature size. Desirably, the ultraviolet radiation strikes the wafer with its electric field vector parallel to the wafer surface so that interference occurs in the plane of the wafer. In low-NA imaging applications, the polarization of the beam is relatively unimportant; because the beam strikes the wafer at substantially normal incidence, any beam polarization will have its electric field vector parallel to the wafer. In high-NA imaging applications, such as are used in state-of-the-art microlithography systems used to make microelectronic devices, radiation can strike the wafer at a relatively oblique angle. At higher angles, the polarization of the ultraviolet radiation becomes important. See, for example, B. W. Smith et al., “Benefiting from polarization—effects on high NA imaging,” Proc. SPIE, vol. 5377, pp 68-79, which is incorporated herein by reference in its entirety. As such, a desirable device would provide ultraviolet radiation with a tailorable polarization distribution. Further, the excimer lasers often used in ultraviolet photolithography, while having high power at low wavelengths, tend to produce an asymmetric beam with many ‘hot spots.’ A desirable device would also provide ultraviolet radiation having a tailorable intensity distribution.